Locking the fronts only with my Big Red's

[westcoast911]

1988 Carrera, with a Big Red Kit from Race Technologies circa 2004 with a price tag of about $5700 Race Technologies I have attached the invoice because when I tried to figure out exactly what I had it never came up as the part number is no longer any good. I think its a kit that is no longer available. The rotors are cross drilled which seems really blingy to me,so I don't get that part either.

The P.O installed these about 10 years and 30K miles before selling me the car.

I have never driven a Carrera with stock brakes hard,so I don't have a baseline to compare to. For a few different reasons I have on more than one occasion considered removing the kit and re installing the stock brakes(came with car)

If you look at the invoice attached it looks as though a 23.81mm 930 Master has also been installed.

I am looking for some advice on dealing with front wheel lock up that has me nervous about pushing the car. I have always driven a heavy sedan, and like the feel of lots of rear brake so it may just be me adjusting to a rear engine car. Either way,I want more rear brake and less lock.

Tires on the car admittedly are not the best,so i think I could hide some of the problem with new rubber, however I believe that the car should have a more neutral or rear biased brake feel than it currently does.

How can I get there?? OK, I couldn't upload the invoice so here are the Part #'s 1B16001R2 BREMBO BIG RED GTP2 FRONT KIT 2C16002R2 BREMBO BIG RED GTP2 REAR KIT 93035501103 MASTER CYLINDER

[tctnd]

If it has an adjustable bias valve (it should) you can try opening it a bit to increase the rear bite. If they are so unbalanced that you can't find a satisfactory setting, you will need rear calipers with more piston area or fronts with less.

regards,
Phil

[Joe Bob]

Too much front brake. Adjustable bias or more aggressive rear brakes......

[westcoast911]

Originally Posted by tctnd

If it has an adjustable bias valve (it should) you can try opening it a bit to increase the rear bite. If they are so unbalanced that you can't find a satisfactory setting, you will need rear calipers with more piston area or fronts with less.

regards,
Phil

Bias is not adjustable

[0396]

Great looking car...you need to have a rear bias installed in the rear.. If it were me, I would call Race Tech for advice. They are great to deal with. If your in Van, you might look up a Porsche shop in Langley - I think the owner is Jeff ...as he post here.
Good luck

[westcoast911]

I have been in contact with Jeff to ask about my cars set up. The PO had given me a ledge file of records and notes with the car,but couldn't remember much about the set up, Jeff's name was mentioned several times.

Its come to my attention that maybe some info on the suspension might be helpful in solving this issue.

As far as I know, the car has upgraded torsion bars ( 21/27mm )

Shocks are Bilstein sports, I believe the car is sitting at Euro ride height. Has 17x8 and 17x9 wheels with 225/45 and 255/40 tires. Im still getting used to the car, and the tires are done.

Fronts seem to lock under any panic stop and at anything over about 60%. From 60MPH if you jump on the pedal, rather than haul the car down the fronts just lock. I can modulate around it,but it feels like a recipe for me to crash at my first track day with the car.

[0396]

I'm no expert, but fronts should not lock up while stopping from 60 mph. You really need to get a brake bias to control the rears...that's what I did when I put the same set- up on my 914.

[westcoast911]

I think brake bias control is so you can limit the amount of rear brake,seems to me we need the opposite here.

I need less front brake and more rear.

[0396]

Originally Posted by westcoast911

I think brake bias control is so you can limit the amount of rear brake,seems to me we need the opposite here.

I need less front brake and more rear.

Correct. I adjusted the rear until it would slightly lock up.

One other possibilities is that the fronts have more aggressive compound pads.

[westcoast911]

You really need to get a brake bias to control the rears-

With no rear bias control in place,I currently have full rear braking capacity. Adding a bias adjuster to the rear circuit will not increase the amount of rear brake,it will simply allow me to dial more rear brake out,which would make the current condition worse.

Agreed that pad selection may also have an effect, I believe the pads in place currently are stock OEM front and rear

[Joe Bob]

You can install a valve in the brake line....

[Porboynz]

Interesting problem, how much rear brake do you really want? Having the fronts lockup before the rears is more preferable to having the rears lockup first on a 911, but it sounds like you have way too much capability up front. Do both fronts lock evenly and does the car stay straight? Time to try harder pads up front and softer pads at the rear if you want to reduce that front lockup, otherwise stock brakes will restore the factory setup and balance. Having said that, a call to Race Technologies might solve the problem quicker, maybe there was a rear bias valve fitted with the kit and its seized or otherwise faulty, have you eyeballed the entire brake system? A rear bias valve could be tucked away out of sight above the gearbox somewhere. Got to get it fixed, great brakes are a big part of the Porsche experience.

[Steve@Rennsport]

You have the GTP brakes, NOT the Big Red (aka 993TT brakes). These have a fair amount of built-in front bias and along with the front Sport Bilsteins (too much front bump valving), aggravate the propensity for front lockup.

These are really nice brakes that may simply need the addition of a Tilton manual bias adjuster (lever style) into the front brake circuit to provide the adjustability you need.

Before you do ANYTHING, make sure the factory rear brake pressure limiter thats standard on all Carrera's has been removed.

There are other things to do as well, however I cannot offer anything further without knowing something about your driving skills and experience.

[westcoast911]

Originally Posted by Steve@Rennsport

You have the GTP brakes, NOT the Big Red (aka 993TT brakes). These have a fair amount of built-in front bias and along with the front Sport Bilsteins (too much front bump valving), aggravate the propensity for front lockup.

These are really nice brakes that may simply need the addition of a Tilton manual bias adjuster (lever style) into the front brake circuit to provide the adjustability you need.

Before you do ANYTHING, make sure the factory rear brake pressure limiter thats standard on all Carrera's has been removed.

There are other things to do as well, however I cannot offer anything further without knowing something about your driving skills and experience.

This is great Steve- can you tell me te difference between the GTP and the 993 TT?

Where is the factory brake limiter located? I think you may have hit on something previously overlooked.

My experience has been in solo 1 and 2 since 1999, but all of that was done in a car I built myself, a 600HP early second gen Fbody. A very challenging car to be quick in,but easy for me to control, and totally different from a 911.

I have no skill or experience in a 911, but love the car so far. I miss the power oversteer of my old car, but the 911 feels much more stable at higher speeds.

[westcoast911]

Originally Posted by Porboynz

Interesting problem, how much rear brake do you really want? Having the fronts lockup before the rears is more preferable to having the rears lockup first on a 911, but it sounds like you have way too much capability up front. Do both fronts lock evenly and does the car stay straight? Time to try harder pads up front and softer pads at the rear if you want to reduce that front lockup, otherwise stock brakes will restore the factory setup and balance. Having said that, a call to Race Technologies might solve the problem quicker, maybe there was a rear bias valve fitted with the kit and its seized or otherwise faulty, have you eyeballed the entire brake system? A rear bias valve could be tucked away out of sight above the gearbox somewhere. Got to get it fixed, great brakes are a big part of the Porsche experience.

I'm used to left foot braking in my old car to help it rotate, so I like having substantial rear brake. That being said I like all 4 wheels to lock if that going to happen at all and with this car it's very clearly just the fronts long before the rears come to the party. Time to look a little closer for a hidden bias valve.

[javadog]

Two suggestions. Tires that have little grip will make this worse, as they lock before you transfer much weight to the front. New tires would help.

Secondly, you may be able to change your technique a little. Be more progressive in getting on the brakes. Jumping on them hard is not what you want to do with those.

JR

[john walker's workshop]

the carrera bias valve is under the triangle cardboard piece between the master cylinder and the smuggler's box.

[Bill Verburg]

I've looked at 3 different GTP setups not counting the GTP/L which was pretty nice

Most likely what you have is the Kit w/ F40 front calipers, and Lotus rear calipers on 993tt 322mm rotors f/r w/ a 930 m/c

I have feedback from multiple owners, all of it along the lines of what the OP has reported, some have led to serious accidents

torque bias for the F40/Lotus GTP kit is very much front 2.03, for referencea ll 911 before Porsche started messing w/ bias in '84 were 1.491

You should never use a p/v on the front

and w/ your current setup be sure to remove the stock one on the rear circuit

there are 2 things that you can do to alleviate the issue
1) lower the front bias w/ a caliper w/ smaller pistons, a 993RS/tt front(aka Big Red) bolts on w/the correct adapter and lowers torque bias to 1.856
2) raise rear bias, a 993 rear caliper can be adapted w/ a little work, a 965 rear can be adapted w/ a little less work, either of these will lower the bias w/ 993RS/tt front to 1.520. A 993RS rear can also be adapted and is far more difficult to do but that will lower the bias to 1.426

I don't understand why RaceTech sold that kit, the previous version was Big Red(993tt/RS) all around and was fantastic as long as you got the 993RS rear calipers, form what I understand some came w/ 993 tt rears which would be as bad as the GTP kit

[westcoast911]

Originally Posted by Bill Verburg

I've looked at 3 different GTP setups not counting the GTP/L which was pretty nice

Most likely what you have is the Kit w/ F40 front calipers, and Lotus rear calipers on 993tt 322mm rotors f/r w/ a 930 m/c

I have feedback from multiple owners, all of it along the lines of what the OP has reported, some have led to serious accidents

torque bias for the F40/Lotus GTP kit is very much front 2.03, for referencea ll 911 before Porsche started messing w/ bias in '84 were 1.491

You should never use a p/v on the front

and w/ your current setup be sure to remove the stock one on the rear circuit

there are 2 things that you can do to alleviate the issue
1) lower the front bias w/ a caliper w/ smaller pistons, a 993RS/tt front(aka Big Red) bolts on w/the correct adapter and lowers torque bias to 1.856
2) raise rear bias, a 993 rear caliper can be adapted w/ a little work, a 965 rear can be adapted w/ a little less work, either of these will lower the bias w/ 993RS/tt front to 1.520. A 993RS rear can also be adapted and is far more difficult to do but that will lower the bias to 1.426

I don't understand why RaceTech sold that kit, the previous version was Big Red(993tt/RS) all around and was fantastic as long as you got the 993RS rear calipers, form what I understand some came w/ 993 tt rears which would be as bad as the GTP kit

I'm going to make a second call to race tech on Monday and see what they have to say.
Bill, from a performance perspective, would I be better served re installing the OEM Carrera brakes? Are there some simple mods that could make the stock pieces more effective? They did come with the car as well.

[Bill Verburg]

Originally Posted by westcoast911

I'm going to make a second call to race tech on Monday and see what they have to say.
Bill, from a performance perspective, would I be better served re installing the OEM Carrera brakes? Are there some simple mods that could make the stock pieces more effective? They did come with the car as well.

Unless you are tracking the car yes, stock Carrera are going to be fine, the bigger brakes mostly give you thermal capacity that is never used on the street, you do get more brake torque but since stock brakes can lock the wheels and it's the tires that are stopping the car it's not really useable w/o all the other track car mods